More is known about the neuromuscular synapse than any other synapse. Its geometrical simplicity and experimental assessibility have provided us with a relatively detailed account of what a synapse looks like and how a synapse functions. We remain, however, rather poorly informed about the biochemical events involved in the formation and maintenance of this highly specialized and organized region of cell-to-cell contact. This proposal is concerned with further characterization of three proteins which we have identified as components of the subsynaptic sarcoplasm at nerve-muscle synapses. Although we do not yet know the function of these proteins, their location suggests that they may have a role in the formation and/or maintenance of the synapse. We will use chemical cross-linking reagents and monoclonal and antibodies to determine whether these subsynaptic proteins interact with each other and/or with subunits of the acetylcholine receptor. We will use antibodies against these subsynaptic proteins to determine when these proteins appear at synapses which are forming in vivo and in vitro; such information may provide clues about the function of these subsynaptic proteins. We will determine whether injection of antibodies to the subsynaptic proteins into muscle cells interferes with structure and function of the synapse. We will also determine the effect of the subsynaptic proteins on the open time and conductance of acetylcholine receptor channels which have been reconstituted into planar bilayers.